3214 BROADWAY Geotech Report 2022-10-25

American Property Development ES-0599.06 June 9, 2016 Page 12 Revised October 16, 2017 Retaining Walls Retaining walls should be designed to resist earth pressures and any applicable surcharge loads. For design of the garage level foundation walls, the previous earth pressure values provided for cantilever and multiple tieback shoring walls should be used, as appropriate for yielding and restrained wall conditions. These earth pressure values were previously provided in the Shoring Recommendations section of this study. With respect to site retaining walls constructed independent of the building foundation walls at or near existing site grades, the following values should be used for design: Site Retaining Walls • Active Earth Pressure (Yielding Wall) 35 pcf(equivalent fluid /granular fill) • At-Rest Earth Pressure (Restrained Wall) 50 pcf • Traffic Surcharge (Passenger Vehicles) 70 psf(rectangular distribution) • Passive Resistance 350 pcf(equivalent fluid) • Allowable Soil Bearing Capacity 4,000 psf(preliminary) • Coefficient of Friction 0.40 Additional surcharge loading from foundations, sloped backfill, or other loading should be included in the retaining wall design, as appropriate. Drainage should be provided behind retaining walls such that hydrostatic pressures do not develop. If drainage is not provided, hydrostatic pressures should be included in the wall design, as appropriate. The geotechnical engineer should review retaining wall designs to verify that appropriate earth pressure values have been incorporated into the design and to provide additional recommendations, as necessary. Retaining walls should be backfilled with free draining material that extends along the height of the wall, and a distance of at least 18 inches behind the wall. The upper one foot of the wall backfill can consist of a less permeable (surface seal) soil, if desired. In lieu of free draining backfill, use of an approved sheet drain material can also be considered, based on the observed subsurface and groundwater conditions. The geotechnical engineer should review conditions at the time of construction and provide recommendations for sheet drain, as appropriate. A perforated drain pipe should be placed along the base of the wall, and connected to an appropriate discharge location. Where foundation walls are formed against the temporary shoring walls, the shoring wall drainage illustrated on Plate 6 can be utilized. For site retaining walls receiving backfill, the retaining wall and drainage detail illustrated on Plate 7 should be considered. Earth Solutions NW,LLC